PubMed Health⌕ Search

Biomedical subjects

S Iyobe

Publications and source records attributed to S Iyobe.

69 records · Page 4Linked to original sources
PubMed1974

Relationship between chloramphenicol acetyltransferase activity and the number of resistance genes.

Various mutants of an Escherichia coli K-12 strain were prepared, in which a chloramphenicol (CM) resistance gene (cml) derived from an R factor, R100-1, was integrated into the chromosome. The CM acetyltransferase (CATase) activity of these strains and the strain carrying R100-1 were determined during exponential growth with the following results. (i) The CATase activity varied, depending upon the site of integration of the cml gene on the chromosome. Activity was found to be higher when the cml gene was integrated nearer the replication origin of the chromosome, the total enzyme activity found was the sum of activities coded by each gene separately. (iii) When the cml gene was in a cytoplasmic state on an R factor, R100-1, the expressed enzyme activity was four-to eightfold higher than that in the chromosomal state, suggesting the existence of about four to eight copies of R factor per chromosome. The CATase activity returned to the level of that expressed by R100-1 when the chromosomal cml gene was detached and picked up by an R factor.

Acetyltransferases↗
PubMed1974

Demonstration of R factors from Pseudomonas aeruginosa.

Sixty strains of Pseudomonas aeruginosa were selected from our clinical stock cultures and used as donors of drug resistance to examine the presence of R factors. They were highly resistant to one or more of six drugs including tetracycline (TC), chloramphenicol (CM), streptomycin (SM), sulfanilamide (SA), carbenicillin (CPC), and kanamycin (KM). Three FP(-), auxotrophic mutants of P. aeruginosa were used as recipients, which had been made resistant to either rifampin (RMP) or KM by in vitro mutation. Each donor was mated with each of the three recipients, and 45 strains were found to transfer their resistance to one or more recipients. A second series of conjugation experiments using 45 exconjugants as donors showed that 23 could transfer their resistance. We conclude that these strains carry R factors that are transmissible to one or more recipients. Eleven carried resistance to (TC.CM.SM.SA.CPC), nine to (TC.CM.SM.SA), one to (TC.CM.SA.CPC), one to (TC.CM.SA), and one to (SM). All of these R factors could not be transmitted to other species belonging to the family Enterobacteriaceae.

Anti-Bacterial Agents↗
PubMed1973

Sex pili mutants isolated by macarbomycin treatment.

Macarbomycin (MM) preferentially kills Escherichia coli carrying episomes derepressed for sex pili formation (drd episomes). Using MM, we have isolated various types of mutants from both F-lac.tet and R100-1 episomes and have classified them into two types by sex pili formation. Among 26 mutants, 20 could not produce pili and had lost both the ability for conjugal transmission and sensitivity to male phages. From 12 of these 20 mutants, revertants capable of pili formation could be obtained. Most of these had simultaneously regained susceptibility to MM, indicating that the MM susceptibility of E. coli carrying drd episomes is due to pili formation. Three of the revertants could not confer MM susceptibility on their host and two of them could not produce normal pili, indicating that there are some types of pili insensitive to MM. The six MM-resistant mutants could produce pili, but the frequency of pili formation was slightly lower than that of their parent episomes. Mutants of this type exhibited various degrees of decrease in conjugal transferability or male phage sensitivity, and one mutant produced pili that were altered in shape. It is suggested that this latter mutant became MM-resistant as a result of changes in the chemical composition of its pili.

Anti-Bacterial Agents↗